One-step process for making a polymer composite coating with high barrier

ABSTRACT

This invention relates to a a one-step process for making a polymer composite suspension for coating plastic films characterized in that a first polymer is synthesized in-situ optionally in the presence of other polymers and in the presence of clay. Preferably the polymer composite suspension comprises a)  1.0  to  11.0  wt % of clay or silane modified clay, b)  0.1  to  10.0  wt % of poly (acrylic acid), which is a copolymer of acrylic acid (AA) with at least one other monomer selected from  2 -ethylhexyl acrylate (EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethyl ethylene urea (WAM II) and ethoxylated behenyl methacrylate (β-FM), c)  1.0  to  15.0  wt % of other polymers, preferably poly (vinyl alcohol) and d)  70  to  97  wt % of water or mixture of water with  2 -propanol. The coating films made from the suspensions show good barrier capabilities against water vapor and oxygen can be used to make barrier layers on or within plastic films for packaging applications. The invention also relates to methods for making silane modified clay usable in the process for making the suspensions.

TECHNICAL FIELD

The present invention generally relates to a process for makingclay/polymer composites as a barrier layer for plastic films via aone-step process.

BACKGROUND ART

Plastic films such as Polyethylene terephthalate (PET), polypropylene(PP) and polyethylene (PE) are extensively used in packaging due to lowcost, strength and stiffness, transparent and flexibility properties. Inpackaging, specifically for food packaging applications, a good barrierlayer against oxygen and moisture is important to prolong the shelf lifeof packaged food. Oxygen and moisture that transmit from surroundingenvironment into the packaging will accelerate the oxidation andspoilage of food and encourage rapid mold growth during storage andtransportation periods. Despite having a good mechanical strength andmoldability properties, the barrier performance of commerciallyavailable plastic films in the market today is still relatively poor.

Polymer composites have been developed mainly to improve the mechanicalproperties and barrier performance of polymers to moisture and gasessuch as oxygen and carbon dioxide. Polymer composites are mixtures ofpolymers with inorganic or organic fillers with certain geometries.Inorganic fillers with a high aspect ratio such as nanoclay areparticularly interesting because of their high specific surface area,availability, low cost, significant reinforcing effects and simpleprocessability. According to Nielsen's theory (1967), the presence ofnanoclay fillers in polymer matrix increases the tortuosity of thediffusive path for a penetrate molecule, thus providing an excellentbarrier property. In recent years, many research works have beenconducted on the modification of clay surfaces with organic compoundssuch as silanes with the aim to maximize the barrier performance byimproving nanoclay compatibility with polymers. Besides the barrierperformance, mechanical integrity of composite film and its bondingstrength to plastic substrate are further factors affecting compositepackaging performance.

The preparation methods and coating solutions for making composite filmsknown from the prior art preferably make use of silane modified claycomposites. However, the preparation methods for such modified clay arenot satisfying. As known from the prior art, it is generally difficultto dissolve or disperse silanes in aqueous clay suspension because oftheir organophilic nature. To overcome this problem, previous approacheshave used additives such as surfactants to form silane emulsions priorto the reaction with an aqueous clay suspension. The silane is firstemulsified into water containing surfactant, which acts as a wettingagent and emulsifier. Then, the emulsified silanes are mixed with theclay silicates. Accordingly, the surfactant used in this case is limitedto a specific range of hydrophilic/lipophilic balance valises. Inaddition, the surfactant concentration and pH at which thesilane/surfactant emulsion is prepared are very important to theresulting silane emulsion stability. By using this method, it is verydifficult to mix different types of silanes into one pot of aqueous claysuspension in a one-step process, because there a reaction may occurbetween the two silanes before reacting with clay silicates, which willresult in reduced surface treatment of clay and bonding strength to thepolymer matrix. Moreover, the presence of residual surfactants in thefinished silane modified clay product may influence the properties ofbarrier layer even though its concentration is low. All these parameterslimit the efficacy of the process and productivity in their preparation.

Another known method is directed to dissolving or dispersing silanesinto aqueous clay suspension via a solvent exchange technique. In thismethod, the clay silicate aqueous suspension may be subjected to asolvent exchange whereby the solvent is capable of dissolving the silanecompound. The solvent may be an organic solvent selected from methanol,ethanol, propanol, butanol, or pentanol or ketone, propanone or2-butanone. The solvent exchange method involves washing and filtrationsteps. After silane-clay reaction, the solvent is removed and the silanemodified clay is redispersed in aqueous solution. This modificationprocess is cumbersome and may increase manufacturing cost. It furtherinvolves the use of organic solvent which makes it less environmentallyacceptable.

In summary, it is found that the barrier films known from the prior artare not fully satisfying with regard to bonding strength to plasticfilms or do not show the desired high transparency. Others are verycumbersome to prepare and require the use of emulsifier/surfactant ororganic solvent during the preparation.

Therefore, there is still a need to provide more cost effective, timesaving and environmentally friendly methods to produce clay/polymercomposite films with good oxygen and moisture barrier property combinedwith good bonding strength that overcome, or at least ameliorate, one ormore of the disadvantages described above.

SUMMARY OF INVENTION

According to a first aspect, there is provided a one-step process formaking a polymer composite suspension for coating plastic filmscharacterized in that a poly (acrylic acid) (PAA) copolymer issynthesized in-situ optionally in the presence of other polymers and inthe presence of clay. Advantageously, the invention provides a poly(acrylic acid) copolymer that can be synthesized by in-situpolymerization and shows improved barrier performance and bondingstrength of the resulting polymer/clay composites on plastic films. Thebarrier layer of the present invention can be used for making barriersin plastic films with high transparency.

In one embodiment, the other polymers are selected from poly (vinylalcohol). The suspension made by the process can comprise 1.0-10.0 wt %of clay , optionally 0.05-1.0 wt % of silanes, 0.1-10.0 wt % of poly(acrylic acid), 1.0-15.0 wt % of poly (vinyl alcohol) and 70-97 wt % ofwater or mixture of water with 25 wt % of 2-propanol. These compositionsshow a very high bonding strength and barrier properties.

In another embodiment the poly (acrylic acid) copolymer is a blockcopolymer synthesized from a mixture of acrylic monomers. A mixture ofacrylic monomers comprising acrylic acid (AA), 2-ethylhexyl acrylate(EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethyl ethyleneurea (WAM II) and ethoxylated behenyl methacrylate (β-EM) is preferred.Advantageously, the variation of acrylic monomers and their content inthe mixture allow the specific improvement of the suspensions. It wasfound that the β-CEA block, longer pendant carboxylic acid chainsfacilitate PAA/Clay and PAA/plastic bonding. It was further found thatUreido rings in WAM II block enhance PAA/Clay and PAA/plastic bondingstrength. It was also found that the self-assembly of hydrophobicaliphatic chains from β-EM will enhance the moisture barrier ofPVA/PAA/CIay composite coating.

In another embodiment the following sequence of steps is used: a)dissolving the other polymers, such as e.g. PVA, in water, b) adding theacrylic monomers under stirring, c) adding a dispersion of clay in waterunder high speed homogenisation, and d) starting a radicalpolymerisation in the presence of a starter and inert gas under elevatedtemperature to obtain a suspension. Advantageously, this in-situpolymerisation sequence is well suited to make the improved barrierlayers.

Further embodiments relate to the use of radical starters selected frombenzoyl peroxide, butyl hydro peroxide, azobisisobutyronitril or acombination of butyl hydro peroxide and isoascorbic acid in thepolymerisation of the PAA copolymer and the use of silane modified clay.Advantageously, in the case of the use of silane modified clay, the claysheets can be chemically coupled to the polymer matrix by silanecoupling agents. In another embodiment the clay is modified with a blendof amino silanes and glycidoxy silanes. This mixture of silane couplingagents advantageously improves the clay dispersion into polymer. It maystrengthen the bonding by providing crosslinking as the alkoxy reactivegroup of the silane binds to the clay silicate and the epoxy and aminereactive group may be made available for binding to the polymer in thepolymer matrix. The addition of both aminosilanes and glycidoxy silanesis a method to further improve the bonding strength and adhesion to thepolymer, thereby forming a strong composite layer.

According to a second aspect of the invention, there is provided therespective polymeric coating suspension obtainable according to theprocess of the invention.

According to a third aspect of the invention, there is provided arespective polymer composite coating suspension comprising

a) 1.0 to 11.0 wt % of clay or silane modified clay,

b) 0.1 to 10.0 wt % of poly (acrylic acid) copolymer, which is acopolymer of acrylic acid (AA) with at least one other monomer selectedfrom 2-ethylhexyl acrylate (EHA), β-carboxyethyl acrylate (β-CEA),methacrylamidoethyl ethylene urea (WAM II) and ethoxylated behenylmcthacrylate (β-EM),

c) 1.0 to 15.0 wt % of other polymers and

d) 70 to 97 wt % of water or mixture of water with of 2-propanol.

These suspensions advantageously show good bonding to plastic films,high transparency and flexibility combined with high water vapour andoxygen protection when being coated on plastic films. In one embodimentthe other polymers in this suspension are selected from poly (vinylalcohol) and block copolymers of ethylene and vinyl alcohol.

According to a fourth aspect of the invention there is provided a methodfor making the silane modified clay by dispersing the clay in an aqueoussolution and adding a silane or a mixture of silanes at a slow injectionspeed under high homogenization speed. Preferably the silane or silanemixture is added by injection with a flow rate of 0.1 to 3.0 ml/min andthe speed of homogenization is in the range of 15,000 to 20,000 rpm of aturrax. Advantageously, this allows to uniformly intercalate silanesinto clay sheet suspension in the high speed homogenization process. Thesilane is directly dispersed into aqueous clay suspension without usingsurfactants or organic solvent. With the present invention, it isfeasible to prepare silane mixture modified clay product in a one-stepprocess.

According to a fifth aspect, the invention relates to the use of silanemodified clay obtained in a process for making a polymeric coatingsuspension for forming a barrier film on plastic films which comprises apolymer that has at least a hydroxyl functional group, a polymer thathas a carboxyl functional group or mixtures thereof. Advantageously, thesilane modified clay can be used in such a broad range of processes formaking such polymer matrices including the in-situ polymerisationprocess mentioned above.

According to a sixth aspect, the invention relates to polymeric coatingsuspension obtained by using the silane modified clay made according tothe above described method.

According to a seventh aspect of the invention, the polymeric coatingsuspensions made according to the various inventive processes andmethods can be used for producing a laminated film on a plasticsubstrate. In one embodiment the use comprises the following steps: a)applying an inventive polymer composite suspension on a plastic film viablade coating, b) drying the obtained barrier layer on the plastic film,and c) coating the obtained bi-layer film with at least another plasticsubstrate with adhesive. The resulting three or more layer film obtainedcan be used for making packaging films. Advantageously, the packingfilms show the improved moisture and oxygen barrier capabilities.

DEFINITIONS

The following words and terms used herein shall have the meaningindicated:

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionincludes all such variations and modifications. The invention alsoincludes all of the steps, features, compositions and compounds referredto or indicated in this specification, individually or collectively, andany and all combinations or any two or more of said steps or features.

The term “clay” refers to both naturally occurring clay materials and tosynthetic clay materials. Clay refers to phyllosilicate minerals and tominerals which impart plasticity and which harden upon drying or firing.See generally, Guggenheim, S. & Martin, R. T., “Definition of Clay andClay Mineral: Joint Report of the AIPEA Nomenclature and CMSNomenclature Committees,” Clays and Clay Minerals 43:255-256 (1995).Materials composed of clay are characterized by having a mineralstructure formed by the arrangement of octahedral units and tetrahedralunits or by stacked layers formed by an octahedral sheet and one or moretetrahedral sheets of the atoms that constitute the clay structure.Illustrations are the two groups of naturally occurring clay minerals.First is the hormite group, defined here as including palygorskite andsepiolite, which have channels formed by octahedral units andtetrahedral units of the clay mineral structure. Second is the smectitegroup including montmorillonites and saponite, which are constituted bystacked layers formed by an octahedral sheet and more than onetetrahedral sheet, and mixtures of the foregoing. Smectite is a genericterm that refers to a variety of related minerals also found in someclay deposits. Smectite is composed of units made of two silicatetrahedral sheets with a central alumina octahedral sheet. Each of thetetrahedra has a tip that points to the center of the smectite unit. Thetetrahedral and octahedral sheets are combined so that the tips of thetetrahedra of each silica sheet and one of the hydroxyl layers of theoctahedral sheet form a common layer. In particular, the smectite familyof clay minerals includes the various mineral species montmorillonite,beidellite. nontronite, hectorite and saponite, all of which can bepresent in the clay mineral in varying amounts.

The term “synthetic clay” is to be interpreted broadly to includematerials related in structure to layered clays and porous fibrous clayssuch as synthetic hectorite (lithium magnesium sodium silicate). Theterm “synthetic clay” may include materials that have the same chemicalformula and structure as natural clays.

Unless specified otherwise, the terms “comprising” and “comprise”, andgrammatical variants thereof, are intended to represent “open” or“inclusive” language such that they include recited elements but alsopermit inclusion of additional, unrecited elements.

As used herein, the term “about”, in the context of concentrations ofcomponents of the formulations, typically means +/−5% of the statedvalue, more typically +/−4% of the stated value, more typically +/−3% ofthe stated value, more typically, +/−2% of the stated value, even moretypically +/−1 % of the stated value, and even more typically +/−0.5% ofthe stated value.

Percentages in a composition refer to weight percentages unless statedotherwise.

Throughout this disclosure, certain embodiments may be disclosed in arange format. It should be understood that the description in rangeformat is merely for convenience and brevity and should not be construedas an inflexible limitation on the scope of the disclosed ranges.Accordingly, the description of a range should be considered to havespecifically disclosed all the possible sub-ranges as well as individualnumerical values within that range. For example, description of a rangesuch as from 1 to 6 should be considered to have specifically disclosedsub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4,from 2 to 6, from 3 to 6 etc., as well as individual numbers within thatrange, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of thebreadth of the range.

Certain embodiments may also be described broadly and geneticallyherein. Each of the narrower species and subgeneric groupings fallingwithin the generic disclosure also form part of the disclosure. Thisincludes the generic description of the embodiments with a proviso ornegative limitation removing any subject matter from the genus,regardless of whether or not the excised material is specificallyrecited herein.

DETAILED DISCLOSURE OF EMBODIMENTS

Non-limiting embodiments of the invention will be further described ingreater detail by reference to specific examples, which should not beconstrued as in any way limiting the scope of the invention.

According to a first aspect, there is provided a one-step process formaking a polymer composite suspension for coating plastic filmscharacterized in that a poly (acrylic acid) (PAA) copolymer issynthesized in-situ optionally in the presence of other polymers and inthe presence of clay.

The final polymer composite suspension may be a gelatinous suspension ofclay/polymer(s), wherein the clay is present in the gelatinoussuspension. The term “gelatinous suspension” is to be interpretedbroadly to refer to a liquid composition whereby one of the constituentsin the liquid composition is present in a particulate semisolid form inthe suspension.

The clay silicates may be selected from the group consisting ofmontmorillonite, bentonite, laponite, kaolinite, saponite, vermiculiteand mixtures thereof. The clay may be natural clay, synthetic clay orsilane or silane mixture modified clay. In a preferred embodiment, theclay is montmorillonite. The clay preferably has a sheet-type orplate-like structure and a high aspect ratio. The clay sheets are only afew nanometers, sometimes only about 1 nm, thick (nanoclay).

The clay content in the polymer composite suspension is preferablybetween 1 wt % and 10 wt %, between 1 wt % and 8 wt %, between 1 wt %and 6 wt %, between 1 wt % and 5 wt %, between 1 wt % and 3 wt %,between 1 wt % and 2 wt %, between 2 wt % and 10 wt %, between 3 wt %and 10 wt %, between 5 wt % and 10 wt %, between 8 wt % and 10 wt %.

In one embodiment the clay is a silane modified clay. In the embodimentof silane modified clay, clay may be chemically coupled to the polymermatrix by a silane coupling agent or mixtures thereof with othersilanes. The silane content in the suspensions is then between 0.05 and1.0 wt %, preferably 0.05 to 0.7 wt %, most preferably 0.05 to 0.2 wt %.Preferred are silanes with a glycidoxy group for coupling. Inembodiments where coupling compound is glycidoxy silane, the glycidoxysilane compound may be a glycidoxyalkylalkoxysilane compound or aglycidoxyalkylsilane compound. The glycidoxyalkylalkoxysilane compoundmay be selected from the group consisting ofglycidoxymecthyltrimethoxysilane, glycidoxymethyltricthoxysilane,glycidoxymethyltripropoxysilane, glycidoxyethyltrimethoxysilane,glycidoxyethyltriethoxysilane, glycidoxyethyltripropoxysilane,glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane,glycidoxypropyltripropoxysilane, glycidoxypropyltri (methoxyethoxy)silane, glycidoxypropylmethyldimethoxysilane,glycidoxypropylmethyldiethoxysilane,glycidoxypropylmethyldiethoxysilane,glycidoxypropylmethyldibutoxysilane,glycidoxypropylmethyldiisopropenoxysilane,glycidoxypropyldimethylethoxysilane,glycidoxypropyldimethylmethoxysilane,glycidoxypropyldimethylpropoxysilane,lycidoxypropylmethyldiisopropenoxysilane,glycidoxypropyldiisopropylethoxysilane, glycidoxypropylbis(trimethylsiloxy) methylsilane, glycidoxybutyitrimethoxysilane,hydrolyzates thereof, and mixtures thereof. The glycidoxyalkylsilanecompound may be at least one of glycidoxypropyltrimethylsilane andglycidoxypropylpentamethyldisiloxane. Additional exemplaryglycidoxysilane compounds may be obtained from U.S. Pat. No. 5,115,069.

The silane can be applied at a weight ratio of 1 to 30 %, preferably 2to 20%, most preferably 3 to 17% by weight relative to the clay.

The coupling agent may also be an aminosilane, such as an(aminoalkyl)trimethoxy silane coupling agent or mixtures thereof withother silanes. Most preferably silane coupling agent may be(3-glycidoxypropyl)trimethoxysilane, (3-aminopropyl)trimethoxysilane andmixtures thereof. A mixture of (3-aminopropyl)trimethoxysilane and(3-glycidoxypropyl)trimethoxysilane at a concentration ratio of about1:5 to 4:5 and more preferably at a concentration ratio of about 2:3 maybe particularly mentioned as preferred to achieve a good bondingstrength.

In one embodiment, clay is dispersed in aqueous solution. It ispreferable to add a small volume of acetic acid to promote exfoliationof clay sheets in the suspension.

The amount of clay in the final barrier layer after coating a plasticfilm with the suspension and drying may be in the range selected fromthe group consisting of between 20 wt % and 80 wt %, between 25 wt % and80 wt %, between 30 wt % and 80 wt %, between 40 wt % and 80 wt %,between 50 wt % and 80 wt %, between 55 wt % and 80 wt %, between 60 wt% and 80 wt %, between 70 wt % and 80 wt %, between 20 wt % and 30 wt %,between 20 wt % and 35 wt %, between 20 wt % and 40 wt %, between 20 wt% and 45 wt %, between 20 wt % and 50 wt %, between 20 wt % and 55 wt %,between 20 wt % and 60 wt %, between 20 wt % and 65 wt %, and between 20t % and 70 wt %, based on the weight of the polymer matrix. In otherembodiments the amount of clay in the barrier layer made from thepolymer composite suspension is in the range of 20 to 80 wt % based onthe weight of polymer matrix, more preferably in the range of 20 to 60wt %, and particular preferably in the range of 20 to 40 wt %. Thehomogeneous dispersion of high concentration clay sheets that arewell-oriented along the polymer matrix does not affect the opticalproperties of the barrier layer.

Poly(acrylic acid) (hereinafter also PAA) includes in its meaning allsynthetic high molecular weight polymers of acrylic acid. According tothe invention it can be a block copolymer of various acrylic monomers.The PAA content in the polymer composite suspension is preferablybetween 0.1 wt % and 10 wt %, between 0.1 wt % and 4 wt %, between 0.1wt % and 2 wt %, between 0.1 wt % and 1 wt %, between 0.5 wt % and 2 wt%, between 0.5 wt % and 7 wt %, between 0.5 wt % and 5 wt %, between 0.5wt % and 4 wt %, between 0.5 and 1, between 1 wt % and 4 wt %. The PAApreferably has a Molecular weight (MW) of 200,000-600,000 g/mol, morepreferably 400,000-500,000 g/mol, most preferably 450,000 g/mol.

Optionally the PAA polymer matrix may comprise other polymers or aplurality of other polymers that may be capable of cross-linking witheach other to form the polymer matrix. Preferably, the polymer (s)making up the polymer matrix may have at least a hydroxyl functionalgroup, a carboxyl functional group and/or an amine functional group. Thehydroxyl group and carboxyl group may be disposed on the ends of apolymer chain, or on the side-chains of the backbone of a polymer chain.In addition, this polymer may include an amine functional group. Inanother embodiment where a plurality of polymers is used, each polymermay have the hydroxyl functional group, the carboxyl functional group orthe amine functional group.

In the embodiment where the hydroxyl group and carboxyl group are on thesame polymer chain as end groups or on the side-chains of the backboneof a polymer chain, this polymer may be selected from the groupconsisting of vinyl alcohol-acrylic acid copolymer and vinylalcohol-methacrylic acid copolymer.

When other polymers are used together with the PAA, the polymer having ahydroxyl functional group may be selected from the group consisting ofpolyvinyl alcohol polymer, polyvinyl alcohol derivatives, polyvinylalcohol copolymers, starch, starch derivatives, chitosan, chitosanderivatives, cellulose, cellulose derivatives such as cellulose etherand ester derivatives, gums, arabinans, galactans, galactomannans,proteins, various other polysaccharides and mixtures thereof. Thepolymer having a carboxyl functional group may be a polycarboxylic acid.The polymer having an amine functional group may be selected from thegroup consisting of alkylated polyallylamine, polyvinylamine, poly(diallylamine) and poly (ethyleneimine), optionally substituted at oneor more nitrogen atoms with an alkyl group or a substituted alkyl groupsuch as a trialkylammonioalkyl group.

As at least one of the other polymers used according to the first aspectof the invention poly (vinyl alcohol) (hereinafter also PVA) ispreferred. The polyvinyl alcohol polymer comprises mainly monomer unitsof vinyl alcohol. The polyvinyl alcohol copolymer may poly(ethylene-co-vinyl alcohol) (EVOH) of varying vinyl alcohol content. PVAcan be a water-soluble synthetic polymer. It has then the idealizedformula [CH₂CH(OH)]_(n). The PVA preferably has a molecular weight (MW)of 1,000 to 100,000, more preferably 20,000 to 60,000, most preferably40,000 to 50,000.

The PVA content in the polymer composite suspension is preferablybetween 1 wt % and 15 wt %, between 1 wt % and 12 wt %, between 1 wt %and 10 wt %, between 1 wt % and 7 wt %, between 1 wt % and 5 wt %,between 4 wt % and 8 wt %, between 3 wt % and 9 wt %, between 2 wt % and8 wt %, between 2 wt % and 15 wt %, between 5 wt % and 15 wt %, between8 wt % and 15 wt %, between 10 wt % and 15 wt %, between 12 wt % and15wt %.

Preferably the PAA copolymer is the result of a polymerisation ofvarious acrylic monomers or monomer blocks comprising acrylic acid,2-ethylhexyl acrylate, β-carboxyethyl acrylate, methacrylamidoethylethylene urea and ethoxylated behenyl methacrylate. The weightpercentage of various blocks in the polymer preferably comprise 50 to 90wt %, more preferably 55 to 80 wt %, most preferably 60 to 70 wt % ofacrylic acid. The monomer mixture preferably comprises 5 to 30 wt %,more preferably 5 to 25 wt %, most preferably 10 to 20 wt % of2-ethylhexyl aery late. The monomer mixture preferably comprises 0.5 to10 wt %, more preferably 1 to 7 wt %, most preferably 3 to 5 wt % ofβ-carboxyethyl acrylate. The monomer mixture preferably comprises 0.5 to10 wt %, more preferably 1 to 7 wt %, most preferably 3 to 5 wt % ofmethacrylamidoethyl ethylene urea. The monomer mixture preferablycomprises 0.5 to 10 wt %, more preferably 1 to 7 wt %, most preferably 3to 5 wt % of ethoxylated behenyl methacrylate.

The PAA co-polymer is novel and also part of the invention.

If PVA is used as another polymer, the PVA to PAA ratio is preferablyabout 10:1 to 1:10, more preferably 8:1 to 1:1, most preferably 5:1 to2:1.

The polymer composite suspension made according to the inventive processpreferably comprises between 70 wt % and 97 wt %, between 90 to 97 wt %or between 92 and 96 wt % of water or a water or a mixture of water with2-propanol. Deionized water or deionized water in admixture of 25 wt %of 2-propanol may be especially mentioned.

The suspension made by the process can therefore comprise 1.0 to 10.0 wt% of clay, optionally 0.05 to 1.0 wt % of silanes, 0.1 to 10.0 wt % ofpoly (acrylic acid), 1.0 to 15.0 wt % of poly (vinyl alcohol) and 88 to97 wt % of water or mixture of water with 25 wt % of 2-propanol.

Another composition to be mentioned is one that comprises 1.0 to 10.0 wt% of clay, 0.05-1.0 wt % of silanes, 0.1-10.0 wt % of poly(acrylicacid), 1.0-15.0 wt % of poly(vinyl alcohol), 70-97 wt % of deionisedwater or mixture with 25 wt % of 2-propanol.

According to a second aspect of the invention, there is provided therespective polymeric coating suspension obtainable according to theprocess of the invention.

An especially preferred suspension according to the invention comprises

a) 1.0-11.0 wt % of clay or silane modified clay,

b) 0.1-10.0 wt % of poly (acrylic acid), which is a copolymer of acrylicacid (AA) with at least one other monomer selected from 2-ethylhexylacrylate (EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethylethylene urea (WAM II) and ethoxylated behenyl methacrylate (β-EM),

c) 1.0-15.0 wt % of other polymers and

d) 88-97 wt % of water or mixture of water with of 2-propanol.

The components of a) to d) may add up to 100% of the suspension. Thispolymer composite coating solution suspension is novel and also part ofthe invention.

Component c) can preferably be selected from poly (vinyl alcohol). Acomposition is preferred which contains all of the acrylic monomersselected from 2-ethylhexyl acrylate (EHA), β-carboxyethyl acrylate(β-CEA), methacrylamidoethyl ethylene urea (WAM II) and ethoxylatedbehenyl methacrylate (β-EM).

As mentioned above, the monomer mixture of all monomers or blockmonomers preferably comprises 50 to 90 wt %, more preferably 55 to 80 wt%, most preferably 60 to 70 wt % of acrylic acid. The monomer mixturepreferably comprises 5 to 30 wt %, more preferably 5 to 20 wt %, mostpreferably 10 to 20 wt % of 2-ethylhexyl acrylate. The monomer mixturepreferably comprises 0.5 to 10 wt %, more preferably 1 to 7 wt %, mostpreferably 3 to 5 wt % of β-carboxyethyl acrylate. The monomer mixturepreferably comprises 0.5 to 10 wt %, more preferably 1 to 7 wt %, mostpreferably 3 to 5 wt % of methacrylamidoethyl ethylene urea. The monomermixture preferably comprises 0.5 to 10 wt %, more preferably 1 to 7 wt%, most preferably 3 to 5 wt % of ethoxylated behenyl methacrylate. Themonomers and block monomers above may add up to 100 wt %.

Other components and preferred use ratios have been also discussed abovewith regard to the suspension of the one-step process according to thefirst aspect of the invention.

The suspension obtained is stable and can be stored for longer periodsof time, such, as more than 180 days.

Preferably the process comprises the following steps:

a) optionally dissolving the other polymers in water

b) adding the acrylic monomers or monomer blocks of the poly (acrylicacid) copolymer into water or into the aqueous polymer solution understirring,

c) adding a dispersion of clay in water,

d) starting a radical polymerisation in the presence of a starter andinert gas under elevated temperature to obtain a suspension.

In step a) PVA or its mixtures with other polymers is preferred as thepolymer to be dissolved in water. Preferably this is done at elevatedtemperatures of about 60 to 95° C. and under stirring. Step a) can beoptional, if no other polymers are used in addition to PAA.

In step b) the components are mixed into the aqueous solution.Preferably the monomers comprise a mixture of acrylic acid, 2-ethylhexylacrylate, β-carboxyethyl acrylate, methacrylamidoethyl ethylene urea andethoxylated behenyl methacrylate. Then, preferably the 2-ethylhexylacrylate is added first and separately.

In step c) the addition of clay suspension in water is preferably doneunder or followed by a homogenization. In the clay/water dispersionacetic acid can be used for exfoliating the clay sheets.

Step d) is a radical polymerisation. The radical polymerisation ispreferably performed at elevated temperature of about 50 to 95° C. inthe presence of a radical starter. The radical starter can be anysuitable starter for radical polymerisation of the monomers to form PAAcopolymer. As such starters there can be mentioned peroxide and azocompounds, such as for example benzoyl peroxide (BPO), butyl hydroperoxide (BHPO), azobisisobutyronitril (AIBN) or a combination of butylhydro peroxide and isoascorbic acid. The polymerization is initiated byheating the monomer suspension to the elevated temperature in thepresence of inert gas, such as nitrogen. In the suspensionpolymerization, PVA works as emulsifier to encapsulate acrylate monomerand clay works as emulsion aider to stabilize acrylate monomersuspension. Step d) can be run in an emulsion to form the finalsuspension.

Steps a) to d ) can be run without separation steps (“one pot process”).

In another aspect of the invention there has been provided a method formaking silane modified clay that can be preferably used in the inventiveprocess for making the coating suspensions. A method is provided formaking silane modified clay by dispersing the clay in an aqueoussolution and adding a silane or a mixture of silanes at a slow injectionspeed under high homogenization speed.

The dispersion of clay into water can be preferably done by stirringover several hours, preferably 3 to 8 hours and can be supported byultrasonication. For exfoliation acetic acid can further be added in theclay/water dispersion after the first stirring and/or ultrasonication.After addition of the acetic acid the dispersion is preferably stirredagain for several hours, preferably 6 to 24 hours to obtain an optimalstarting material for silane modification.

In one embodiment of this method, the silane is then introduced to thedispersed clay suspension via slow flow rate injection technique, whilethe clay suspension is continuously mixed under high speed duringhomogenization process. Preferably the flow rate of the injection of thesilane is between 0.1 to 3.0 ml/min, more preferably at 0.1 to 1.0ml/min, and particularly preferably at 0.1 to 0.5 ml/min. The injectioncan for example be made to a specified volume in a 300 ml to 1 l roundbottom flask. The homogenization speed is preferably in the range of10,000-20,000 rpm, preferably 15,000 to 20,000 rpm of a suitabledisperses A typical lab disperser, such as an IKA® T 18 digitalULTRA-TURRAX®, can be used with an adequate high speed setting. Forexample, in case of a combined (3-aminopropyl)trimethoxysilane and(3-glycidoxypropyl)trimethoxysilane use, (3-aminopropyl)trimethoxysilaneis first slowly injected into the clay suspension, followed by slowinjection of (3-glycidoxypropyl)trimethoxysilane. In one embodiment, theclay suspension is continuously mixed under high speed during thehomogenization process while both injections are carried out. The silanemodified clay suspension is then allowed to further homogenize for asufficient time, preferably of about 5 to 30 min, more preferably about15 minutes, for the silane or silanes to bind to the surfaces of thesilicate sheets.

The method according to the invention for making the silane modifiedclay comprises preferably a heating step after the injection of thesilane. In this heating step, an elevated temperature is applied.Typical temperatures are for instance about 80° C. or less, or about 40to 75° C. In an embodiment, an aqueous silanes modified clay suspensionmay be heated at about 50 to 70° C. for about 3 to 8 hours, preferably 3to 6hours, under stirring.

The silane modified clay obtained according to the method can bedirectly used in a process for making a polymeric coating suspension forforming a barrier film on plastic films which comprises a polymer thathas at least a hydroxyl functional group, a polymer that has a carboxylfunctional group or mixtures thereof. In an embodiment, the polymerhaving a hydroxyl functional group may be selected from the groupconsisting of polyvinyl alcohol polymer and its derivatives. The polymerhaving a carboxyl functional group may be selected from the groupconsisting of polycarboxylic acid and its derivatives such aspolyacrylic acid polymer. The polymer matrix is preferably a mixturethereof for an optimum reinforcement. The amount of polymer in thebarrier layer may be in the range of 20 to 80 wt %, based on the weightof clay, more preferably in the range of 50 to 70 wt %.

The silane modified clay obtained according to method can also bedirectly used in the one-step process according to the first aspect ofthe invention.

The polymer composite suspensions obtained in the one-step processaccording to the first aspect of the invention or the silane modifiedclay obtained by the above described method can be used for producing alaminated film on a plastic film.

A process for the preparation of polymer composites water-based coatingsuspensions of the invention may comprises the steps of a ) preparing ofa silane modified clay or a silane blend modified clay b) homogeneouslymixing with water soluble polymer solutions c) coating on a plasticfilm. Thereby a barrier layer is formed.

All the polymer composite coating suspensions described above can befurther used for producing a laminated film comprising said polymercomposite suspensions together with an adhesive.

The plastic film which is coated or laminated with the suspension canfor instance be a polyethylene terephthalate, biaxially orientedpolypropylene or polyethylene film, coated with about 5 to 50 μm of saidpolymer composites coating solution. The final concentration of barrierlayer may be in the range of about 1 to 10 wt %, more preferably in therange of about 3 to 8 wt %, and particularly preferably of about 5 to 7wt % of the overall coated film. In one embodiment, the finalconcentration of the barrier layer from the polymer composite suspensionis about 7 wt %. After drying, the coated harrier layer will be about0.25 to 3.5 μm in thickness. The concentration of clay/polymer may becalculated by measuring the weight change, of a part of the compositessuspension before and after complete drying. The silanes modifiedpolymer composite suspension can be applied onto plastic film via bladecoating using a film applicator to form a composites layer thereon.

A bilayer structure of (silane modified clay/polymer composite)/plasticcan be obtained. The clay sheets are homogeneously dispersed in the saidcomposites and aligned along the substrate plane by employing theshearing force during the application. The applied said composites layeron the plastic substrate is then dried by air flash at room temperature,and the heating step is more preferably followed by vacuum drying atabout 60° C. or hot air drying.

Step e) can comprise the following steps: applying the polymer compositesuspension on a plastic film via blade coating, drying the obtainedbarrier layer on the plastic film, and coating the obtained bi-layerfilm with at least another plastic substrate with adhesive.

At least another layer of plastic substrate is then coated with adhesiveas binder to improve the adhesion between two films. The applied saidadhesive/plastic bilayer is dried by air flash at room temperature. Inone embodiment, the heating step is undertaken when the said (silanesmodified clay/polymer composite)/plastic bilayer film is compressedtogether with said adhesive/plastic to form a plastic/(silane modifiedclay/polymer composites)/plastic trilayer film which can be covered byadditional layers. The temperature used during the heating step may bein the range of about 100 to 140° C. depending on the plastic substrateused. In one embodiment, the temperature applied is about 130° C. for apolyethylene terephthalate substrate. The heating step may he alaminating step. It is preferable to apply pressure during thelamination process.

The laminated plastic/(silanes modified clay/polymer composites)/plastictrilayer film allows light to pass through the film. The tri or morelayer film obtained has use for making packaging films.

The transparency of the film can be influenced by the concentration ofcomposites and the thickness of the barrier layer. Process optimizationto produce a thin barrier layer with a thickness of less than 5 μm,preferably a thickness which is below 1 μm is desirable for uses inpackaging to fulfil the requirements of low material usage and low filmthickness combined with excellent transparency.

EXAMPLES

Non-limiting examples of the invention and a comparative example will befurther described in greater detail by reference to specific Examples,which should not be construed as in any way limiting the scope of theinvention.

Materials and Methods

In the examples described below, unless otherwise indicated, alltemperatures in the following description are in degrees Celsius and allparts and percentages are by weight, unless indicated otherwise.Reagents useful for synthesizing compounds may be purchased fromcommercial suppliers as mentioned in the examples.

Test Methods Used Oxygen Transmission Rate (OTR)

Oxygen permeability of nanocomposites coated PET film was measured byusing Mocon oxygen permeability OX-TRAN Model 2/21 according to ASTMD3985standard. Each film was placed on a stainless steel mask with anopen testing area of 5 cm². Oxygen permeability measurements wereconducted at 23° C. (1 atm) and 0% relative humidity by placing coatedsurface of films to the oxygen rich side.

Water Vapor Transmission Rate (WVTR)

Water vapor permeability of nanocomposites coated PET film was measuredby using Mocon water vapor permeability PERMATRAN-W Model 3/33 accordingto ASTM F1249 standard. Each film was placed on a stainless steel maskwith an open testing area of 5 cm². Water vapor permeabilitymeasurements were conducted at 37.8° C. (1 atm) and 90% relativehumidity by placing coated surface of films to the water vapor richside.

Example 1 Preparation of Silanes Modified Clay Suspension (SMMT[1])

5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. ofArlington Heights of Ill. of the United States of America was mixed with125 ml deionised water and stirred for 6 hours, followed byultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml ofacetic acid was added to the solution and stirred for another 12 hours.To exchange water with acetone, acetone was added to the suspension. Theclay suspension was homogenized with acetone using an IKA T18 BasicUltra Turrax homogenizer at 15,000 rpm for 5 minutes. Thereafter, theslurry precipitate was filtered with a Buchner funnel and washed withacetone. The collected slurry precipitate was re-suspended into 500 mlof acetone and homogenized for 5 minutes at 15,000 rpm, followed byfiltration and washing. Each cycle should use at least 500 ml ofacetone. After second cycle, the collected precipitate was transferredto a round bottom flask, and then topped up with appropriate amount ofacetone, 0.1 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) and0.15 g of (3-glycidoxypropyl)trimethoxysilane (³ 98%, Aldrich) wereadded to the solution. After stirring for 8 hours at room temperature,the mixture was ultrasonicated for 30 minutes and stirred at 50° C. for8 hours. Then, 125 ml of deionized water was added intoclay-acetone-silanes mixture and all the acetone was then removed byrotary evaporation at 60° C.

Example 2 Preparation of Silanes Modified Clay Suspension (SMMT[2])

5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. ofArlington Heights of Illinois of the United States of America was mixedwith 125 ml deionised water and stirred for 6 hours, followed byultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml ofacetic acid was added to the solution and stirred for another 12 hours.After that, 0.1 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) wasfirst slowly injected (0.1 ml/min) into the clay suspension, followed by0.15 g of (3-glycidoxypropyl)trimethoxysilane (³ 98%, Aldrich) underhigh speed of homogenizing process at 15,000 rpm by using an IKA T18Basic Ultra Turrax for 15 minutes. Then, silanes modified claysuspension was heated at 50° C. for 6 hours under stirring.

Example 3 Preparation of Silanes Modified Clay Suspension (SMMT[3])

5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. ofArlington Heights of Illinois of the United States of America was mixedwith 125 ml deionised water and stirred for 6 hours, followed byultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml ofacetic acid was added to the solution and stirred for another 12 hours.After that, 0.2 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) wasfirst slowly injected (0.1 ml/min) into the clay suspension, followed by0.3 g of (3-glycidoxypropyl)trimethoxysilane (³ 98%, Aldrich) under highspeed of homogenizing process at 15,000 rpm by using an IKA T18 BasicUltra Turrax for 15 minutes. Then, silanes modified clay suspension washeated at 50° C. for 6 hours under stirring.

Example 4 Preparation of Silanes Modified Clay Suspension (SMMT[4])

5.0 g of pristine clay (montmorillonite) obtained from Nanocor Inc. ofArlington Heights of Illinois of the United States of America was mixedwith 125 ml deionised water and stirred for 6 hours, followed byultrasonication in a water-bath for 30 minutes. Then, 0.1875 ml ofacetic acid was added to the solution and stirred for another 12 hours.After that, 0.3 g of (3-aminopropyl)trimethoxysilane (97%, Aldrich) wasfirst slowly injected (0.1 ml/min) into the clay suspension, followed by0.45 g of (3-glycidoxypropyl)trimethoxysilane (³ 98%, Aldrich) underhigh speed of homogenizing process at 15,000 rpm by using an IKA T18Basic Ultra Turrax for 15 minutes. Then, silanes modified claysuspension was heated at 50° C. for 6 hours under stirring.

Example 5 Preparation of Silanes Modified Clay Suspension(SMMT[5]-SMMT[7])

The preparation method is analogous to SMMT[2], except varying the clayto polymer ratio (wt %) and final total solid content concentrations.The composites solution can be diluted with water or mixture of water(75%) and 2-propanol (25%).

Example 6 Preparation of Poly(Vinyl Alcohol) (PVA) Solution

9.76 g of PVA (MW 44,000 completely hydrolyzed obtained from Wako PureChemical Industries, Ltd., Japan) was dissolved in 90 ml of deionizedwater under stirring at 100° C.

Example 7 Preparation of Poly(Acrylic Acid) (PAA) Solution

1.91 g of PAA (MW 450,000 obtained from Polysciences Asia Pacific, Inc.,Taiwan) was dissolved in 23.14 ml of deionized water under stirring atroom temperature (about 25° C.).

Example 8 Preparation of SMMT[2]/Polymer Nanocomposites

First, PAA solution obtained from Preparation Example 7 was added intosilanes modified clay suspension obtained from Preparation Example 2under high speed homogenization process at 15,000 rpm for 5 minutes byusing an IKA T18 Basic Ultra Turrax. Then, followed by addition of PVAsolution obtained from Preparation Example 6 under same conditions.After addition, the mixture was continuously homogenized for 15 minutesat 15,000 rpm. For samples with isopropanol, 25% (v/v) of isopropanol towater may be added into the solution and homogenized for another 5minutes.

Example 9 Preparation of Silanes Modified Clay/Polymer NanocompositesFilm

SMMT[1]-SMMT[7]/Polymer coating solutions obtained from PreparationExample 1-5 were blade coated onto a PET film by using a film applicatorwith an applicator bar coating gap controlled at 50 μm. The appliednanocomposites layer was then dried by air flash at room temperature for24 hours, followed by drying in a vacuum oven at 60° C. for 24 hours.For laminated films, another plastic film is coated with adhesive. Bothof the coated plastic films were compressed together by using alaminator at 130° C.

Example 10 Synthesis of PVA/PAA/Clay Composite Suspension via in situPolymerization

PVA solution is prepared by dissolving 18.4 g PVA into 200 g water at90° C. under stirring. Clay water suspension is prepared by dispersing9.4 g clay into 200 g water under stirring followed by adding 0.3 mlacetic acid and further homogenizing for 30 minutes.

109.7 g of the above prepared PVA solution and 0.5 g EHA (SolvaySingapore Pte Ltd) are added in a 500 ml round bottom flask, and themixture is stirred for 5 minutes. Then 0.1 g P CEA (Solvay Singapore PteLtd), 0.1 g WAM II (Solvay Singapore Pte Ltd), 0.1 g p EM (SolvaySingapore Pte Ltd) and 1.7 g AA (Solvay Singapore Pte Ltd) are mixedinto the PVA solution. 104.7 g clay suspension and 100 g water are addedinto the round bottom flask and homogenized for 5 minutes. Afterinletting N₂ for 30 minutes, the mixture is heated up to 60° C. understirring. Finally, 0.05 ml BHPO and 0.5 ml Isoascorbic acid (5 wt % inwater) are injected into the mixture, respectively, and stirred at 60°C. overnight. The total solid concentration of the prepared PVA/PAA/Clay composite suspension is 4.4 wt %.

OTR and WVTR of PET film coated with the above prepared PVA/PAA/Claycomposite suspension are measured as 0.46 cc/m²·day and 19.2 g/m²·day,respectively: OTR and WVTR of PP film coated with the above preparedPVA/PAA/Clay composite suspension are measured as 1.3 cc/m²·day and 4.4g/m²·day, respectively.

Results

Table 1 showed the transmission rate of oxygen and water vapor forplastic films with or without composites coating. Oxygen transmissionrate was measured at 23° C. and 0% relative humidity, and water vaportransmission rate was measured at 37.8° C. at a 90% relative humidityfor a number of test films. The thickness of the composites layer iscontrolled in a range of about 0.3 to 3.5 μm, which is dependent on thefinal total solid content concentration. Meanwhile, the thickness of aPET plastic film is about 12 μm. As revealed in Table 1, the oxygentransmission rates of composites layer coated PET films weresignificantly reduced in comparison to that of pure PET film. In thepresent invention, the lowest OTR of the composites/plastic film wasachieved at 0.19 cc/(m2·day ), which in overall is 99.7 to 99.9% ofreduction as compared to pure PET film. On the other hand, the watervapor transmission rates of composites layer coated plastic films werereduced to about 49.3 to 72.4% in comparison to that of pure PET film.In addition, the barrier property of composites layer prepared frompresent invention (SMMT

TABLE 1 Oxygen and Water Vapor Transmission Rates of Films Silanes toSolid Clay/polymer dry clay content ratio OTR (cc/[m². WVTR Type ofFilm* (wt %) (wt %) (wt %) day]) (gm/[m² · day]) PET — — — 130.65 46.49SMMT[1]_Polymer/PET 5 7 30/70 0.33 15.02 SMMT[2]_Polymer/PET 5 7 30/700.30 12.89 SMMT[3]_Polymer/PET 10 7 30/70 0.24 12.85 SMMT[4]_Polymer/PET15 5 30/70 0.19 14.43 SMMT[5]_Polymer/PET 5 5 30/70 0.28 14.85SMMT[6]_Polymer/PET 5 4 50/50 0.31 17.50 SMMT[7]_Polymer/PET 5 4 75/250.22 23.55 *Thickness of the composite layer was controlled at about2.5-3.5 μm

INDUSTRIAL APPLICABILITY

The one-step process for making polymer composite suspensions may find amultiple number of applications in the manufacturing of barrier filmsfor plastic films of packaging. For example, the methods as definedabove may be used to manufacture packaging films with good barrierproperty. A good barrier layer against oxygen and moisture is importantto protect the produces packaged from fast oxidation and deterioration.With the present invention, a barrier layer against oxygen and moisturecan be made. It is to be appreciated that the presence of silanemodified clay/polymer composites layer coated on the plastic substratemay substantially inhibit the permeation of gases and water vapormolecules to pass through the film. It is envisaged that silanesmodified clay sheets that well intermix with polymer matrix form ahierarchical structure, which creates a longer tortuous path formolecules diffusion. The composites may also adsorb and retain part ofthe molecules on the surfaces, thus resulting in a reduced transmissionrate of gas and water vapor molecules. Moreover, the laminatedcomposites film is mechanically flexible to contour for multiplepackaging applications due to the bending ability of the film.

It will be apparent that various other modifications and adaptations ofthe invention are available to the person skilled in the art afterreading the foregoing disclosure without departing from the spirit andscope of the invention and it is intended that all such modificationsand adaptations come within the scope of the appended claims.

1.-11. (canceled)
 12. A polymeric coating suspension that comprises: a)1.0 to 11.0 wt % of clay or silane modified clay, b) 0.1 to 10.0 wt % ofpoly (acrylic acid) copolymer, which is a copolymer of acrylic acid (AA)with at least one other monomer selected from 2-ethylhexyl acrylate(EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethyl ethyleneurea (WAM II) and ethoxylated behenyl methacrylate (β-EM), c) 1.0 to15.0 wt % of other polymers and d) 70 to 97 wt % of water or mixture ofwater with 2-propanol.
 13. The suspension according to claim 12, whereinpoly (acrylic acid) is derived from a monomer mixture that comprises: a)50 to 90 wt % of acrylic acid, b) 5 to 30 wt % of 2-ethylhexyl acrylate,c) 0.5 to 10 wt % of β-carboxyethyl acrylate, d) 0.5 to 10 wt % ofmethacrylamidoethyl ethylene urea, e) 0.5 to 10 wt % of ethoxylatedbehenyl methacrylate.
 14. A method for making silane modified clay bydispersing the clay in an aqueous solution and adding a silane or amixture of silanes at a slow injection speed under high homogenizationspeed.
 15. The method according to claim 14 wherein the silane or silanemixture is added by injection with a flow rate of 0.1 to 3.0 ml/min. 16.The method of according to claim 14 wherein the speed of homogenizationis in the range of 10,000 to 20,000 rpm.
 17. The method according toclaim 14 which comprises a heating step after the addition of thesilanes. 18.-25. (canceled)